Referring to FIG. 1, an example of a conventional pallet system 10 used to support a partially completed vehicle, for example a sheet metal body of a passenger vehicle (not shown) is illustrated. The pallets 10 supported the partial vehicle bodies and are transferred in sequential fashion by a conveyor (not shown) through numerous assembly stations (not shown), for example spot welding and brazing stations, along an assembly line.
In conventional pallets systems 10, a pallet 12 typically included a pair of longitudinal rails 20 oriented along a longitudinal axis 22 (the X coordinate direction) and defining a first end 14 and a second end 16 of the pallet. Crossmembers 26 spanned laterally between the rails 20 along a lateral axis 32 (the Y coordinate direction) defining a rigid pallet structure.
In order to elevate and support the vehicle body, several support beams 30 would be positioned across the rails 20, each support beam 30 including a pair of risers 40 extending vertically along a vertical axis 44 (the Z coordinate direction) as generally shown (four support beams and a total of eight risers 40 shown in FIG. 1 as an example). The number of support beams 30 and risers 40, and position of the support beams 30 and risers 40 depend on the size, length and width of the vehicle body and automotive manufacturer specifications. Although each support beam 30 shows use of two risers 40 per support beam, it is understood that one riser 40, or more than two risers 40 per support beam 30 may be used depending on the application.
As best seen in FIG. 1A, conventional pallet 12 support beams 30 included precision machined locating pads 34 for receipt and mounting of a riser 40 thereon. Risers 40 include a base 46 and several mounting bolts 50 (four shown) for securing each riser 40 to the support beam 30 preventing relative movement between the riser 40 and the support beam 30. An additional locking bolt or dowel 60 (two shown) would be inserted into a predrilled hole through the base 46 and into the support beam 30 to lock the riser 40 in a predetermined position which was an improvement in positional accuracy and repeatability over prior designs. Each riser 40 would include a locating pin 54 (shown in FIG. 1) which would be positioned to engage the vehicle body at predetermined positions on the vehicle body and securely hold the vehicle body in place throughout the various assembly processes.
In vehicle pallet systems, it is of critical importance that the locating pins 54 are positioned accurately and precisely in all three coordinate dimensions X, Y and Z so as to position the vehicle body in known dimensional positions relative to the pallet 12 and the various assembly stations so that precision equipment, for example programmable industrial robots, can carry out various operations on the vehicle body. Current industry dimensional tolerance standards require the locating pins 54 to be within 0.1-0.13 millimeters (mm) from a predetermined design position.
Conventional pallet systems 10 also included a hook and armature linkage inside the risers 40 and locating pins 54 along with actuators 80 positioned on the support beam 30. On rotation of an actuator arm (not shown) at the actuator 80, a linkage 64 positioned across the support beam 30 and inside the hollow riser 40 would manipulate a hook (not shown) positioned inside the hollow locating pin 54 to extend the hook, engage the vehicle body and lock the vehicle body to the riser preventing relative movement of the vehicle body from the risers until the actuator 80 is moved to retract and disengage the hook. An example of a suitable actuator 80 and hook system is described in U.S. Pat. No. 8,839,507 assigned to the present Applicant, the entire contents of which is incorporated herein by reference.
Early prior pallet systems 10 rigidly fixed, for example welded, each support beam 30 and onboard risers 40 to the rails 20 to prevent relative movement of the risers and locating pins 54 from their fixed positions. Due to the many different sizes, lengths and shapes of vehicle bodies, early prior pallet systems 10 could only be used for one vehicle due to the pallet 12's fixed position of the support beams 30, risers 40 and locating pins 54.
In more recent years, an improved pallet design allowed movement of one support beam 30 along the longitudinal axis 22 of rails 20. This would allow a pallet 12 to move one set of risers to a different longitudinal axis 22 (X dimension) in order to accommodate a different vehicle body that had one set of holes in the sheet metal in a different longitudinal position so the pallet could accommodate the vehicle body different hole pattern. However, these improved pallets were only useful for another vehicle body if the same size/diameter riser locator pins 54 were used for both vehicles which also varies from vehicle body model to model. Thus, this improved pallet was also limited in its flexibility to accommodate different vehicle body models and changes in the model production sequence.
In modern vehicle assembly facilities, it is desirable and increasingly common to vary the type or model of vehicles that are assembled along an assembly line. The ability for a manufacturer to change the vehicle styles or bodies being manufactured is highly desirable to meet customer demand for popular vehicle types. In prior assembly facilities, on a vehicle model or style changeover, much of the assembly line equipment and fixtures, for example vehicle pallets 12, would need to be changed to accommodate the new vehicle build. Due to the fixed geometry of prior pallets 12, support beams 30, and risers 40, the entire pallets 12 would need to be removed from the production line and stored or racked until the vehicle production schedule returns to that vehicle style. Typical vehicle pallets 12 are each 5 meters (m)(16.4 feet) long, 1.2 meters (m) (3.9 feet (ft.) wide, and weigh approximately 500 kilograms (kg)(1100 pounds (lb). Thus, movement of the pallets 12 from the assembly line and storage requires heavy equipment and substantial storage space at the assembly facility.
There is a need for an improved vehicle assembly pallet which provides flexibility to rapidly accommodate different vehicle body styles and which maintains the necessary accuracy and precision required of modern vehicle assembly systems.